//This class updated the Hello field on account records that are
// passed to it.
public class MyHelloWorld {
	public static void addHelloWorld(Account[] accs){
		for (Account a:accs){
			if (a.Hello__c != 'World') {
				a.Hello__c = 'World';
			}
		}
	}
	
	public static testMethod void testMyHelloWorld() {
		List<Account> accountList = new List<Account>();
		//create 200 accounts
		for(Integer i=0;i<200;i++) accountList.add(new Account(name = 'i'));
		
		//switch to runtime limit context
		Test.startTest();
		
		//insert the accounts
		insert accountList;
		
		//switch back to the test limit context
		Test.stopTest();
		
		//get the accounts back from the DB and assert the names
		for(Account a:[select Hello__c from Account where id in :accountlist]) {
			System.assertEquals('World',a.Hello__c);
		}
				
	}
}